1. Field of the Invention
The present invention relates to a jet-propulsion personal watercraft (PWC) equipped with an open-loop cooling type engine, and more particularly to control for warming up of the engine.
2. Description of the Related Art
In recent years, so-called jet-propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. The personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a hull bottom surface and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled.
Some types of personal watercraft employ an engine with an open-loop cooling system. In the open-loop cooling system, water such as sea water is taken in from outside the watercraft, pressurized by the water jet pump, and used as cooling water for cooling the engine. In such an engine cooling system, advantageously, the amount of cooling water supplied to the engine by the water jet pump is small at a low engine speed because the water jet pump generates a low supplying pressure for the cooling water. Thus, warming up of the engine is easy. On the other hand, the amount of cooling water is large at a high engine speed because the water jet pump generates a high pressure, and thereby sufficient cooling effect is gained.
However, in the above engine cooling system adapted to take in the water from outside, the engine is sometimes excessively cooled when the temperature of the water is low. In particular, when starting the engine and for a time thereafter, a clearance between a cylinder and a corresponding piston of the engine is small, and in this state, if the engine is operated at a high speed, the engine is subjected to a large frictional load. In such situation, in general, xe2x80x9cwarming upxe2x80x9d is necessary.
In the meantime, an operator of the watercraft has difficulties in judging that sufficient warming up of the engine has been achieved, and sometimes opens a throttle of the engine to increase the engine speed before the completion of sufficient warming up.
The present invention addresses the above-described conditions, and an object of the present invention is to provide a jet-propulsion personal watercraft that employs an open-loop cooling type engine and is capable of executing a control so as not to increase an engine speed before sufficient warming up of the engine has been achieved, irrespective of an operator""s will.
A personal watercraft according to the present invention which is propelled by a water jet pump driven by an open-loop cooling type engine having an open-loop cooling system including a cooling water passage which takes in water from outside the watercraft and uses the water as cooling water for the cooling system. The personal watercraft comprises a control unit adapted to limit an engine speed of the engine to be lower than a predetermined engine speed when a temperature of the cooling water is lower than a first predetermined temperature.
In accordance with the above invention, particularly, in the jet-propulsion personal watercraft equipped with the open-loop cooling type engine, the control is executed so as not to increase the engine speed when the cooling water temperature of the engine is low. This assures the completion of sufficient warming up. The operator is able to know that sufficient warming up of the engine is completed when the engine speed can be increased by, such as trying to open a throttle of the engine. However, the operator cannot increase the engine speed before the completion of sufficient warming up. This prevents the engine under excessively cooled condition from being subjected to a large frictional load.
In the present invention, a time point of the completion of sufficient warming up is defined as when the temperature of the cooling water reaches the first predetermined temperature. To judge whether or not the temperature of the cooling water reaches the first predetermined temperature, the following parameters may be used solely or in combination:
(a) a temperature of the cooling water (direct use),
(b) a temperature of the engine (e.g., temperature of a side face of a cylinder or a surface of a cylinder head), and
(c) a lapsed time from when the engine starts until sufficient warming up is completed, which is measured in advance.
(a) When the cooling water temperature is directly utilized, a temperature detecting means may be attached to any suitable position in the cooling water passage, preferably, in an exit of the cooling water from the engine where a warming up state of the engine is best reflected. By the cooling water temperature detected by the temperature detecting means reaching the first predetermined temperature, it is determined that sufficient warming up of the engine is completed.
(b) Alternatively, when the temperature of the engine is utilized, the temperature detecting means may be attached to any suitable position in the engine, preferably, on an outer surface of the engine cylinder (side face of a cylinder or a cylinder head) which is susceptible to a frictional load in the engine while the engine is excessively cooled. By the temperature of the engine detected by the temperature detecting means reaching a predetermined temperature (corresponding to the cooling water temperature being almost equal to the first predetermined temperature), it is determined that sufficient warming up of the engine is completed. The temperature of the engine for judging the completion of sufficient warming up is easily obtained in such a manner that the engine temperature corresponding to the cooling water temperature at the completion of sufficient warming up is measured in advance and pre-stored in a memory of an ECU (Electronic Control Unit) or the like generally built in the personal watercraft. As for the four-cycle engines, a temperature of lubricating oil may be used instead of the temperature of the cooling water.
(c) The lapsed time from when the engine starts until sufficient warming up is completed is measured in advance, and by clocking the measured time from starting of the engine, it is determined that sufficient warming up is completed. This eliminates a need for temperature measurement during control.
Before completion of sufficient warming up, the control is executed so as to increase the engine speed up to and not to exceed, for example, approximately 3000 rpm. Alternatively, the control may be executed so that the engine speed stays at an idling speed.
At the completion of sufficient warming up, the above limitation of the engine speed may be completely released, or otherwise an upper limit of the engine speed (i.e., the predetermined engine speed) may be increased gradually (e.g., stepwise) according to progress of the warming up.
Further, the limitation of the engine speed may be performed by adjusting fuel injection amount, fuel injection timing and/or ignition timing, or by adjusting a throttle of the engine.
Also, when the cooling water temperature of the engine is higher than a second predetermined temperature which is higher than the first predetermined temperature, the control may be executed to limit the engine speed to be less than the predetermined engine speed.
When the above invention is applied to the personal watercraft which has the engine cooling system using water pressurized by the water jet pump as the cooling water and is susceptible to temperature of the water outside the watercraft, greater effects are obtained.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.